The objective of this study is to determine whether a zidovudine regimen designed to maintain a targeted steady-state concentration is feasible, and whether this approach offers any advantage in terms of safety or anti-retroviral activity over the current standard fixed dose approach. The study is a randomized, crossover, open-label evaluation of these two regimens in HIV-infected individuals. There are no race, gender, or other medication exclusions for participation in this investigation.